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I don't have Address Book 4.1.2, but I expect that Address Book has File, Export, Vcard.
Select All Contacts in the Group column on the left, then click the Name column in the middle, and use Command+A to Select All contacts.
Next, use File, Export, Vcard. All Vcards should be exported into a single file named (by default) Vcards.vcf
Then open Address Book version 5.0.3, use File, Import with the Vcards.vcf file created by version 4.
If you only want to export some of the version 4 contacts, hold the Command key and click on the individual contacts in the Name column to select/deselect them before exporting.